With the dramatic expansion and increased methodologic sophistication in Alzheimer's disease (AD) research, demands on the Clinical Core for clearly defined cohorts of persons with AD and age-matched controls have become more complex. A cohort of subjects appropriate for one type of investigation (such as a clinical treatment outcome trial) is often not appropriate for other types of studies (for example, a case-control epidemiologic study or a genetic linkage analysis) and still other types of cohorts are needed for training clinicians to manage the multiple clinical problems expressed during the course of AD. To meet these multiple demands, the Clinical Core has developed and will continue to provide multiple cohorts of AD patients and normal healthy control subjects suitable for supporting the subject recruitment needs of a broad range of research and clinical training in AD. The intrinsic cohort will continue to include probable AD and nondemented older controls selected for maximum appropriateness for participation in clinical studies and likelihood of obtaining eventual autopsy. The genetic cohort includes patients with familial AD who are followed for participation in linkage analysis and other genetic studies. AD and normal control cohorts extrinsic to but closely linked with the Clinical Core who are appropriate for epidemiologic studies or for clinical training have been developed and will continue to be fostered. In addition, terminally ill nondemented older persons are recruited and characterized to serve as volunteers for donation of control brain tissue. Through these cohorts, subjects are provided to meet the research needs of ADRC investigators, other appropriate investigators in the broader University of Washington research community, and investigators at other institutions.